1. Field of the Invention
The present design relates to the projection of autostereoscopic images, and in particular to producing a strong depth effect for autostereoscopic images received from an autostereoscopic display over a broad range of viewing distances from the display.
2. Description of the Related Art
Autostereoscopic displays use lenticular sheets (and in some cases raster barriers, more or less optically interchangeable with lenticular sheets) as a selection device to enable viewing of a stereoscopic image without the use of individual selection devices (glasses) worn by the observer. The term of art used for these kinds of displays, when more than two views are provided, is “panoramagram,” or sometimes “parallax panoramagram.”
In a panoramagram, multiple perspective views are combined to be imaged by the lens sheet as explained by Okoshi in Three Dimensional Imaging Techniques, NY Academic Press, 1976. In lenticular (or raster barrier) stereoscopic displays, one concern is head movement or user position relative to the display. Head movement in the horizontal direction results in the observer seeing changes of perspective within a viewing zone, where a viewing zone is a spatial region, relative to the display, wherein images on the display are viewed. Perspective views repeat in adjacent viewing zones when transitioning from zone to zone, such as by an observer moving between viewing zones. In other words, the changing perspectives that occur in the primary viewing zone, as one moves laterally, repeats in the secondary and other peripheral zones. These secondary, tertiary, and nth order viewing zones have image quality similar to the primary zone. Beyond the nth order zone, comparative image quality tends to significantly degrade. Performance is symmetrical about the primary zone and the angular extent of the zones is similar. The transition from zone to zone is typically brief with the total of all zones providing the maximum angular extent of viewable image.
As selection occurs at the plane of the screen, many perspective views are required to provide a viewing zone having large angular extent. In the case of a display where only two views are provided, which is sometimes called a parallax stereogram, little head movement is permissible, and the observer's position is restricted. Such restriction of movement is both uncomfortable and undesirable.
The electronic display panoramagram can be adjusted to function well in two different viewing situations. The first is a range of walk-up viewing distances from, for example, 4 to 15 feet away from the display, and also from a distance that is in keeping with, for example, an airport environment where the display is mounted overhead and viewed from 15 feet or more. Currently no panoramagrams commercially available perform well in both scenarios.
Previously available designs therefore have issues with variance in viewer position relative to the display. It would be advantageous to offer a design that enhances or optimizes the autostereoscopic display of images by enabling the viewer to be positioned at various distances from the display.